In a diesel engine, PM (particulate matter) contained in an exhaust as is collected by a collection device arranged in an exhaust pipe through which the exhaust gas passes. In case where the collection device is broken or damaged so that a function is lost, the PM is released to an atmosphere.
In this regard, in an engine, a PM sensor is arranged in the exhaust pipe on the downstream side of the collection device, and an abnormality of the collection device is diagnosed in a manner such that the PM sensor detects the PM flowing out to the downstream side of the collection device. The PM sensor is a sensor which outputs a detection value corresponding to a deposition amount of the PM deposited in the element, and applies a high-voltage current to the element so as to combustion-remove the PM deposited in the element in a case here the deposition amount of the PM exceeds a predetermined value.
Incidentally, in the engine including the collection device, in a case where the deposition amount of the PM collected in the collection device is equal to or more than the predetermined value, a regeneration control is performed which combustion-removes the PM deposited in the collection device by raising a temperature of the exhaust gas passing through the collection device. There is a case where the collection device reaches an excessively high temperature by the regeneration control so as to be partially eroded, whereby a breakage occurs in the collection device, for example, a hole is bored.
Then, in the engine the breakage of the collection device is diagnosed based on a variation of the detection value of the PM sensor arranged at the downstream of the collection device, that is, a variation of a PM content in the exhaust gas having passed through the collection device. However, for example, even in a case where the deposition amount of the PM deposited in the collection device is not close to the predetermined value or the collection device is not broken, when the inflow amount of the PM flowing in the collection device increases, the detection value of the PM sensor arranged on the downstream side is changed by change of an inflow amount of the PM flowing in the collection device, for example, the detection value of the PM sensor arranged on the downstream side also increases. For this reason, a problem occurs in which the breakage of the collection device cannot be diagnosed accurately only by the variation of the detection value of the PM sensor arranged on the downstream side.
With respect thereto, for example, as described in Japanese Unexamined Patent Application Publication No. 2014-185542 (Patent Literature 1), a device is proposed which diagnoses the breakage of the collection device in a manner such that the inflow amount of the PM flowing in the collection device until the PM deposited in the element of the PM sensor arranged on the downstream side is combustion-removed is detected using the detection value of the PM sensor newly arranged in the exhaust pipe on the upstream side of the collection device or a relation obtained in advance by a simulation between an operating condition of the engine and a emission amount of the emitted PM.
In a case where the inflow amount of the PM flowing in the collection device until a predetermined amount of PM is deposited in the PM sensor arranged on the downstream side is small, the device determines that the PM is released from the broken place of the collection device to the downstream side.
However, the PM sensor arranged on the upstream side of the collection device is exposed to the exhaust gas before the PM is collected, so that a lot of PM is deposited in a short time compared to the PM sensor arranged on the downstream side. Thus, the deposited PM is often combustion-removed necessarily, and failure frequency also becomes high since the frequency of combustion-removal is high as well as the inflow amount of the PM cannot be detected accurately.
In the relation between the operating condition of the engine and the emission amount of the PM according to the simulation, enormous data from various factors such as a fuel injection amount, an intake pressure, an intake amount, and a temperature is necessary to improve accuracy. Further, in a case where an integrated value of the inflow amount of the PM flowing in the collection device is calculated, it is necessary to timely calculate the emission amount of the PM which is changed according to the change of the operating condition of the engine, whereby diagnosis becomes complicated.